The present invention relates to an apparatus for automatically polishing mother plates used in the electrolytic recovery of nonferrous metals such as zinc, copper or lead. The apparatus is disposed in a stripping device wherein the deposited metal formed on the mother plates during an electrolysis operation is removed therefrom, and the plates reconditioned so that the mother plates can be transferred back to the electrolytic cells for cyclic use.
Nonferrous metals, such as zinc, copper or lead, are normally refined by electrolytic processes, wherein the desired metal in the ore is leached in the form of an aqueous metallic salt solution which is subsequently electrolized to obtain the metal electro-deposited on cathode plates. In the electro winning of zinc, for instance, a lead plate containing silver is used as the anode and a 99.9% pure aluminum plate as the cathode; an acidic solution of zinc sulphate is electrolyzed for about 24 hours in a cell to produce a deposit of metallic zinc having a desired thickness on the cathode plate, i.e. the mother plate. High purity zinc metal is obtained by stripping the thus deposited zinc metal plate (hereinafter called metal plate) from the cathode mother plates removed from the cell.
In the hydro-metallurgical refining of copper, on the other hand, stainless steel or titanium is used as the mother plate material. In the electro winning of nonferrous metals such as zinc or copper, the aqueous salt solution of the desired metal is first electrolyzed by arranging a plurality of cathode and anode plates alternatively within the cells, and a number of the cathode plates are removed from the cells when the desired metal is deposited on the cathodes after a predetermined period of electrolysis; and the removed cathode metal plates are subsequently transferred by a crane or hoist to the stripping system to remove the deposited metal. The metal plates removed from the cells are stripped of the desired metallic deposits as they are individually carried by a conveyor through the stripping system, and subsequently carried back to the electrolytic cells by a crane or hoist, after a predetermined number of mother plates have accumulated.
The cathode plates, for example, aluminum plates continuously recycled in the electrolysis of zinc, are gradually corroded by the sulfuric acid or traces of florine contained in the electrolyte, resulting in pittings or irregularities on the surfaces thereof. Since such pittings or irregularities in the mother plates cause inhomogeneity of electro deposits, re-dissolution of the deposited metal, or too strong adhesion of the deposited metal on the plate surfaces, thereby inhibiting automatic stripping, it has been the practice to periodically polish manually the surfaces of the mother plates by whetstones or wire brushes before returning the plates to the electrolytic cells.
While stripping systems have recently been mechanized or automated, the periodic polishing of the plates is still currently accomplished by an elaborate method in which the mother plates are individually discharged from the stripping system, making the stripping very complicated. In contrast to conventional polishing in which the mother plates are periodically removed from the stripping process for polishing only upon the appearance of corrosion, the polishing step according to the present invention is mechanized and built into the stripping step permitting fully automated stripping wherein the mother plates, having been stripped of the metallic deposits, are immediately polished while in the stripping system.